The invention is directed to prevent corrosion of a semiconductor device. In the semiconductor device manufacturing method of the invention, a semiconductor substrate is etched from its back surface in a position corresponding to a first wiring formed on the semiconductor substrate with a first insulation film therebetween, to form a first opening exposing the first insulation film. Next, the insulation film exposed in the first opening is etched to form a second opening exposing the first wiring, and then the semiconductor substrate is etched to increase a diameter of the first opening and form a first opening having the larger diameter. Then, a second insulation film is formed on the back surface of the semiconductor substrate including on the first wiring through the first and second openings, and then the second insulation film covering the first wiring is etched.